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Spring as inductive sensor

Christophe Lapiere
Prodigy 20 points

I just read an article about the LDC1000 in the EDN october issue.

They talk about measuring compression, extention and twist of a spring using the LDC1000. 

I didn't find so much informations about this application case in the DS or anywhere.

Is there an application note focused on spring case?

Best regards

Chris

  • 0
    TI__Genius 9300 points

    Hi Chris,

    It's the same basic idea - we just use the spring as an inductor. When the spring deforms, its inductance will change, and LDC1000 will measure the change.

  • 0 in reply to Evgeny Fomin
    TI__Intellectual 1840 points

    Dear Sir,

     what is the mimium inductance could be measured ? Is it possible to detect inductance below 1uH to 100nH ?

    any specical tips in desig and  implemention ?

    regards

    Hawk Tong

  • 0 in reply to Hawk Tong
    Prodigy 20 points

    Hello,

    I've tried with a 250nH (measured with LCR meter) spring and it doesn't work at all.

    Spring dimension : 7.6mm diameter * 20mm length

    Spring turn : N=11

    The little variation of inductance caused by the compression of the spring is not enough to get detect by the LDC1000 even near the Max frequency value.

    The quality factor of the LC tank is bad.

    I am wondering too if there are any tips and tricks for designing an application based on springs.

    BR.

  • 0 in reply to Hawk Tong
    TI__Genius 9300 points

    Hello Hawk,

    Please see FAQ http://e2e.ti.com/support/data_converters/inductive-sensing/f/938/t/295036.aspx#Q2

  • 0 in reply to Christophe Lapiere
    TI__Genius 9300 points

    Hello Christophe,

    Please take a look at this thread:

    http://e2e.ti.com/support/data_converters/inductive-sensing/f/938/p/295756/1040579.aspx#1040579

    While this method is not officially verified by TI yet, it has a lot of merit to it, and worth trying!

  • 0 in reply to Evgeny Fomin
    TI__Genius 9300 points

    Hello Christophe,

    As a side question - did you manage to make this spring to oscillate at all? I would think it's not possible, but again, I do not know the material and wire diameter...

  • 0 in reply to Evgeny Fomin
    Prodigy 10 points

    I only experimented with this a bit, but I found that to get any response at all, I needed to insulate the spring with thinned enamel and use a zinc-plated spring for soldering compatibility. I plan to do further experiments, but my preliminary results weren't promising.

  • 0 in reply to Soumen Nandy
    TI__Genius 9300 points

    Insulating the spring makes perfect sense if the adjacent windings touch each other - there is direct current path, so there is no coil!

    Mechanical solution (crimping/clamping) can be used as an alternative for making contacts to the spring.

    What were the results that you do not find promising? I have successfully tested this application in several configurations.